When human blood circulates through cardio-pulmonary bypass pumps, dialysis machines or through prosthetic valves; physical trauma to the red blood cell is obtained. Shear stress is an important aspect of red cell injury due to mechanical trauma and is known to occur in regurgitant aortic valves and is hypothesized to occur in the normal circulation to a variable degree. Red blood cells can be reproducably damaged by subjecting them to shearing forces in a viscometer. A defect has been found in red cells subjected to low shear stresses. These cells are marked by decreased nucleopore filterability and increased intracellular calcium content, but are normal in appearance. The defect in the subhemolytically sheared red blood cell (SHS-RBC) probably resides in the cell membrane. The aim of the project will be to further characterize the defect present and discover its relationship to the observed increased in red cell calcium content. Shearing of red cells in the presence of calcium or in saline alone and concomitantly determining deformability by nucleopore filtration and intracellular calcium by atomic absorption spectroscopy will decide the importance of increased calcium to the SHS-RBC defect. Studies of the red cell membrane will focus on nucleopore filtration of ghosts to demonstrate altered membrane deformability due to shear. The proteins of the ghost membranes will be characterized by socium dodecylsulfate-polyacrylamide gel electrophoretic techniques. Changes in ghost spectrin extractability, dimer to tetramer ratios and in the mechanical stability of Triton-X produced cytoskeletons will be sought. The in vivo importance of the SHS-RBC will be tested by determining in rabbits the 51Cr labeled red cell half life of cells subjected to several different shear stresses. Studies of persons with prosthetic heart valves or receiving hemodialysis are proposed to demonstrate clinical counterparts of the SHS-RBC.